If you choose an Aura, you also choose a legal permanent for the Copy Enchantment copy of it to enchant. Copy Enchantment doesn’t target that permanent, however, so it can enter the battlefield attached to an untargetable creature.

10/1/2005

If you choose an Aura and there isn’t a legal permanent for it to enchant, you put Copy Enchantment into your graveyard. It never enters the battlefield.

10/1/2005

If you don’t choose an enchantment, Copy Enchantment enters the battlefield without copying anything, and it sits there with a useless ability.

4/1/2006

If this is copying a Genju, such as Genju of the Fields, and the land this enchants goes to the graveyard, you will return the Copy Enchantment to your hand.

7/1/2006

Copies all copiable values, to include mana cost, so if you copy Dream Leash, for example, the converted mana cost of Copy Enchantment will be 5.